Horizontal transfer and phylogenetic distribution of the immune evasion factor tarP.

Methicillin-resistant Staphylococcus aureus (MRSA), a major human pathogen, uses the prophage-encoded tarP gene as an important immune evasion factor. TarP glycosylates wall teichoic acid (WTA) polymers, major S. aureus surface antigens, to impair WTA immunogenicity and impede host defence. However, tarP phages appear to be restricted to only a few MRSA clonal lineages, including clonal complexes (CC) 5 and 398, for unknown reasons. We demonstrate here that tarP-encoding prophages can be mobilized to lysogenize other S. aureus strains. However, transfer is largely restricted to closely related clones. Most of the non-transducible clones encode tarM, which generates a WTA glycosylation pattern distinct from that mediated by TarP. However, tarM does not interfere with infection by tarP phages. Clonal complex-specific Type I restriction-modification systems were the major reasons for resistance to tarP phage infection. Nevertheless, tarP phages were found also in unrelated S. aureus clones indicating that tarP has the potential to spread to distant clonal lineages and contribute to the evolution of new MRSA clones.

Influence of Staphylococcus aureus Strain Background on Sa3int Phage Life Cycle Switches.

Staphylococcus aureus asymptomatically colonizes the nasal cavity of mammals, but it is also a leading cause of life-threatening infections. Most human nasal isolates carry Sa3 phages, which integrate into the bacterial hlb gene encoding a sphingomyelinase. The virulence factor-encoding genes carried by the Sa3-phages are highly human-specific, and most animal strains are Sa3 negative. Thus, both insertion and excision of the prophage could potentially confer a fitness advantage to S. aureus. Here, we analyzed the phage life cycle of two Sa3 phages, Φ13 and ΦN315, in different phage-cured S. aureus strains. Based on phage transfer experiments, strains could be classified into low (8325-4, SH1000, and USA300c) and high (MW2c and Newman-c) transfer strains. High-transfer strains promoted the replication of phages, whereas phage adsorption, integration, excision, or recA transcription was not significantly different between strains. RNASeq analyses of replication-deficient lysogens revealed no strain-specific differences in the CI/Mor regulatory switch. However, lytic genes were significantly upregulated in the high transfer strain MW2c Φ13 compared to strain 8325-4 Φ13. By transcriptional start site prediction, new promoter regions within the lytic modules were identified, which are likely targeted by specific host factors. Such host-phage interaction probably accounts for the strain-specific differences in phage replication and transfer frequency. Thus, the genetic makeup of the host strains may determine the rate of phage mobilization, a feature that might impact the speed at which certain strains can achieve host adaptation.

Impact of Glycan Linkage to Staphylococcus aureus Wall Teichoic Acid on Langerin Recognition and Langerhans Cell Activation.

Staphylococcus aureus is the leading cause of skin and soft tissue infections. It remains incompletely understood how skin-resident immune cells respond to invading S. aureus and contribute to an effective immune response. Langerhans cells (LCs), the only professional antigen-presenting cell type in the epidermis, sense S. aureus through their pattern-recognition receptor langerin, triggering a proinflammatory response. Langerin recognizes the ß-1,4-linked N-acetylglucosamine (ß1,4-GlcNAc) but not α-1,4-linked GlcNAc (α1,4-GlcNAc) modifications, which are added by dedicated glycosyltransferases TarS and TarM, respectively, on the cell wall glycopolymer wall teichoic acid (WTA). Recently, an alternative WTA glycosyltransferase, TarP, was identified, which also modifies WTA with ß-GlcNAc but at the C-3 position (ß1,3-GlcNAc) of the WTA ribitol phosphate (RboP) subunit. Here, we aimed to unravel the impact of ß-GlcNAc linkage position for langerin binding and LC activation. Using genetically modified S. aureus strains, we observed that langerin similarly recognized bacteria that produce either TarS- or TarP-modified WTA, yet tarP-expressing S. aureus induced increased cytokine production and maturation of in vitro-generated LCs compared to tarS-expressing S. aureus. Chemically synthesized WTA molecules, representative of the different S. aureus WTA glycosylation patterns, were used to identify langerin-WTA binding requirements. We established that ß-GlcNAc is sufficient to confer langerin binding, thereby presenting synthetic WTA molecules as a novel glycobiology tool for structure-binding studies and for elucidating S. aureus molecular pathogenesis. Overall, our data suggest that LCs are able to sense all ß-GlcNAc-WTA producing S. aureus strains, likely performing an important role as first responders upon S. aureus skin invasion.

Temperate Phages of Staphylococcus aureus.

Most Staphylococcus aureus isolates carry multiple bacteriophages in their genome, which provide the pathogen with traits important for niche adaptation. Such temperate S. aureus phages often encode a variety of accessory factors that influence virulence, immune evasion and host preference of the bacterial lysogen. Moreover, transducing phages are primary vehicles for horizontal gene transfer. Wall teichoic acid (WTA) acts as a common phage receptor for staphylococcal phages and structural variations of WTA govern phage-host specificity thereby shaping gene transfer across clonal lineages and even species. Thus, bacteriophages are central for the success of S. aureus as a human pathogen.

The C-type lectin receptor MGL senses N-acetylgalactosamine on the unique Staphylococcus aureus ST395 wall teichoic acid.

Staphylococcus aureus is a common skin commensal but is also associated with various skin and soft tissue pathologies. Upon invasion, S. aureus is detected by resident innate immune cells through pattern-recognition receptors (PRRs), although a comprehensive understanding of the specific molecular interactions is lacking. Recently, we demonstrated that the PRR langerin (CD207) on epidermal Langerhans cells senses the conserved ß-1,4-linked N-acetylglucosamine (GlcNAc) modification on S. aureus wall teichoic acid (WTA), thereby increasing skin inflammation. Interestingly, the S. aureus ST395 lineage as well as certain species of coagulase-negative staphylococci (CoNS) produce a structurally different WTA molecule, consisting of poly-glycerolphosphate with α-O-N-acetylgalactosamine (GalNAc) residues, which are attached by the glycosyltransferase TagN. Here, we demonstrate that S. aureus ST395 strains interact with the human Macrophage galactose-type lectin (MGL; CD301) receptor, which is expressed by dendritic cells and macrophages in the dermis. MGL bound S. aureus ST395 in a tagN- and GalNAc-dependent manner but did not interact with different tagN-positive CoNS species. However, heterologous expression of Staphylococcus lugdunensis tagN in S. aureus conferred phage infection and MGL binding, confirming the role of this CoNS enzyme as GalNAc-transferase. Functionally, the detection of GalNAc on S. aureus ST395 WTA by human monocyte-derived dendritic cells significantly enhanced cytokine production. Together, our findings highlight differential recognition of S. aureus glycoprofiles by specific human innate receptors, which may affect downstream adaptive immune responses and pathogen clearance.

Methicillin-resistant Staphylococcus aureus alters cell wall glycosylation to evade immunity.

Methicillin-resistant Staphylococcus aureus (MRSA) is a frequent cause of difficult-to-treat, often fatal infections in humans1,2. Most humans have antibodies against S. aureus, but these are highly variable and often not protective in immunocompromised patients3. Previous vaccine development programs have not been successful4. A large percentage of human antibodies against S. aureus target wall teichoic acid (WTA), a ribitol-phosphate (RboP) surface polymer modified with N-acetylglucosamine (GlcNAc)5,6. It is currently unknown whether the immune evasion capacities of MRSA are due to variation of dominant surface epitopes such as those associated with WTA. Here we show that a considerable proportion of the prominent healthcare-associated and livestock-associated MRSA clones CC5 and CC398, respectively, contain prophages that encode an alternative WTA glycosyltransferase. This enzyme, TarP, transfers GlcNAc to a different hydroxyl group of the WTA RboP than the standard enzyme TarS7, with important consequences for immune recognition. TarP-glycosylated WTA elicits 7.5-40-fold lower levels of immunoglobulin G in mice than TarS-modified WTA. Consistent with this, human sera contained only low levels of antibodies against TarP-modified WTA. Notably, mice immunized with TarS-modified WTA were not protected against infection with tarP-expressing MRSA, indicating that TarP is crucial for the capacity of S. aureus to evade host defences. High-resolution structural analyses of TarP bound to WTA components and uridine diphosphate GlcNAc (UDP-GlcNAc) explain the mechanism of altered RboP glycosylation and form a template for targeted inhibition of TarP. Our study reveals an immune evasion strategy of S. aureus based on averting the immunogenicity of its dominant glycoantigen WTA. These results will help with the identification of invariant S. aureus vaccine antigens and may enable the development of TarP inhibitors as a new strategy for rendering MRSA susceptible to human host defences.

An accessory wall teichoic acid glycosyltransferase protects Staphylococcus aureus from the lytic activity of Podoviridae.

Many Staphylococcus aureus have lost a major genetic barrier against phage infection, termed clustered regularly interspaced palindromic repeats (CRISPR/cas). Hence, S. aureus strains frequently exchange genetic material via phage-mediated horizontal gene transfer events, but, in turn, are vulnerable in particular to lytic phages. Here, a novel strategy of S. aureus is described, which protects S. aureus against the lytic activity of Podoviridae, a unique family of staphylococcal lytic phages with short, non-contractile tails. Unlike most staphylococcal phages, Podoviridae require a precise wall teichoic acid (WTA) glycosylation pattern for infection. Notably, TarM-mediated WTA α-O-GlcNAcylation prevents infection of Podoviridae while TarS-mediated WTA ß-O-GlcNAcylation is required for S. aureus susceptibility to podoviruses. Tracking the evolution of TarM revealed an ancient origin in other staphylococci and vertical inheritance during S. aureus evolution. However, certain phylogenetic branches have lost tarM during evolution, which rendered them podovirus-susceptible. Accordingly, lack of tarM correlates with podovirus susceptibility and can be converted into a podovirus-resistant phenotype upon ectopic expression of tarM indicating that a "glyco-switch" of WTA O-GlcNAcylation can prevent the infection by certain staphylococcal phages. Since lytic staphylococcal phages are considered as anti-S. aureus agents, these data may help to establish valuable strategies for treatment of infections.

Structural and enzymatic analysis of TarM glycosyltransferase from Staphylococcus aureus reveals an oligomeric protein specific for the glycosylation of wall teichoic acid.

Anionic glycopolymers known as wall teichoic acids (WTAs) functionalize the peptidoglycan layers of many Gram-positive bacteria. WTAs play central roles in many fundamental aspects of bacterial physiology, and they are important determinants of pathogenesis and antibiotic resistance. A number of enzymes that glycosylate WTA in Staphylococcus aureus have recently been identified. Among these is the glycosyltransferase TarM, a component of the WTA de novo biosynthesis pathway. TarM performs the synthesis of α-O-N-acetylglycosylated poly-5'-phosphoribitol in the WTA structure. We have solved the crystal structure of TarM at 2.4 Å resolution, and we have also determined a structure of the enzyme in complex with its substrate UDP-GlcNAc at 2.8 Å resolution. The protein assembles into a propeller-like homotrimer in which each blade contains a GT-B-type glycosyltransferase domain with a typical Rossmann fold. The enzymatic reaction retains the stereochemistry of the anomeric center of the transferred GlcNAc-moiety on the polyribitol backbone. TarM assembles into a trimer using a novel trimerization domain, here termed the HUB domain. Structure-guided mutagenesis experiments of TarM identify residues critical for enzyme activity, assign a putative role for the HUB in TarM function, and allow us to propose a likely reaction mechanism.

Cigarette smoking increases the risk for rotator cuff tears.

UNLABELLED: There is little available evidence regarding risk factors for rotator cuff tears. Cigarette smoking may be an important risk factor for rotator cuff disease. The purpose of this study was to determine if cigarette smoking correlates with an increased risk for rotator cuff tears in patients who present with shoulder pain. A questionnaire was administered to 586 consecutive patients 18 years of age or older who had a diagnostic shoulder ultrasound for unilateral, atraumatic shoulder pain with no history of shoulder surgery. Three hundred seventy-five patients had a rotator cuff tear and 211 patients did not. Data regarding cigarette smoking were obtained for 584 of 586 patients. A history of smoking (61.9% versus 48.3%), smoking within the last 10 years (35.2% versus 30.1%), mean duration of smoking (23.4 versus 20.2 years), mean packs per day of smoking (1.25 versus 1.10 packs per day), and mean pack-years of smoking (30.1 versus 22.0) correlated with an increased risk for rotator cuff tear. We observed a dose-dependent and time-dependent relationship between smoking and rotator cuff tears. We observed a strong association between smoking and rotator cuff disease. This may indicate smoking is an important risk factor for the development of rotator cuff tears. LEVEL OF EVIDENCE: Level III, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

Early results of the Ponseti method for the treatment of clubfoot associated with myelomeningocele.

BACKGROUND: Myelomeningocele is a common birth defect that is often accompanied by clubfoot deformity. Treatment of clubfoot associated with myelomeningocele traditionally has consisted of extensive soft-tissue release operations, which are associated with many complications. The purpose of the present study was to evaluate the early results of the Ponseti method for the treatment of clubfoot associated with myelomeningocele. METHODS: Sixteen consecutive patients with myelomeningocele (twenty-eight clubfeet) and twenty consecutive patients with idiopathic clubfeet (thirty-five clubfeet) were followed prospectively while being managed with the Ponseti method. The average duration of follow-up was thirty-four months for the myelomeningocele group and thirty-seven months for the idiopathic group. Clubfoot severity was graded at the time of presentation with use of the Diméglio system. The initial correction that was achieved, casting and/or bracing difficulties, recurrences, and subsequent treatments were evaluated and compared between the two cohorts by means of appropriate statistical analysis. RESULTS: Eleven (39%) of the twenty-eight clubfeet in the myelomeningocele group were graded as Diméglio grade IV, compared with only four (11%) of the thirty-five clubfeet in the idiopathic group (p = 0.014). Initial correction was achieved in thirty-five clubfeet (100%) in the idiopathic group and in twenty-seven clubfeet (96.4%) in the myelomeningocele group (p = 0.16). Relapse of deformity was detected in 68% of the feet in the myelomeningocele group, compared with 26% of the feet in the idiopathic group (p = 0.001). Relapses were treated successfully without the need for extensive soft-tissue release surgery for all but four of the clubfeet in the myelomeningocele group and for all but one of the clubfeet in the idiopathic group (p = 0.16). CONCLUSIONS: Our data support the use of the Ponseti method for the initial treatment of clubfoot deformity associated with myelomeningocele, although attention to detail is crucial in order to avoid complications. Longer follow-up will be necessary to assess the risk of late recurrence and the potential need for more extensive clubfoot corrective surgery in this patient population.

Corticosteroid injection in diabetic patients with trigger finger. A prospective, randomized, controlled double-blinded study.

BACKGROUND: It is generally accepted that the initial treatment for trigger finger is injection of corticosteroid into the flexor tendon sheath. In this study, the efficacy of corticosteroid injections for the treatment of trigger finger in patients with diabetes mellitus was evaluated in a prospective, randomized, controlled, double-blinded fashion and the efficacy in nondiabetic patients was evaluated in a prospective, unblinded fashion. METHODS: Thirty diabetic patients (thirty-five digits) and twenty-nine nondiabetic patients (twenty-nine digits) were enrolled. The nondiabetic patients were given corticosteroid injections in an unblinded manner. The cohort with diabetes was randomized into a corticosteroid group (twenty digits) or a placebo group (fifteen digits). Both of these groups were double-blinded. Additional injections, surgical intervention, and recurrent symptoms of trigger finger were recorded. Treatment success was defined as complete or nearly complete resolution of trigger finger symptoms such that surgical intervention was not required. RESULTS: After one or two injections, twenty-five of the twenty-nine digits in the nondiabetic group had a successful outcome compared with twelve of the nineteen in the diabetic corticosteroid group (p = 0.03) and eight of the fifteen in the diabetic placebo group (p = 0.006). With the numbers studied, no significant difference was found between the diabetic groups. Surgery was performed in three of the twenty-nine digits in the nondiabetic group compared with seven of the nineteen in the diabetic corticosteroid group and six of the fifteen in the diabetic placebo group. There was a significant difference in the prevalence of surgery between the nondiabetic group and both the diabetic corticosteroid group and the diabetic placebo group (p = 0.035 and p = 0.020, respectively). With the numbers studied, no difference was found between the diabetic groups with regard to the persistence of symptoms. Nephropathy and neuropathy were significantly associated with the need for surgery (p = 0.008 and p = 0.03, respectively). CONCLUSIONS: Corticosteroid injections were significantly more effective in the digits of nondiabetic patients than in those of diabetic patients. In patients with diabetes, corticosteroid injections did not decrease the surgery rate or improve symptom relief compared with the placebo. The use of corticosteroid injections for the treatment of trigger finger may be less effective in patients with systemic manifestations of diabetes mellitus.